Order parameter phase sensitive experiments and SDJ dc SQUIDs

Spontaneous generation of persistent dc currents is one of the most strikin g aspects of the physics of superconducting samples in a frustrated geometr y, Trapped vortices, however, are also sources of induced persistent circul ating dc currents. In practice, usually, it is very difficult to establish which of the two is the real source of the observed persistent circulating de currents and their only presence without additional and, very often, com plicated approaches cannot serve as an unambiguous demonstration of frustra tion in a specific geometry. Recently, spontaneous generation of circulatin g ac currents in a frustrated geometry has been predicted. Experimentally o bserved in spatially distributed junctions dc SQUIDs, the effect cannot be reproduced by trapped vortices in the SQUID. Consequently, detection of spo ntaneous circulating ac currents is a straightforward demonstration of frus tration in a given superconducting configuration. For that reason this effe ct can serve as an excellent tool to be used in order parameter phase sensi tive experiments to determine the pairing symmetry of high transition tempe rature superconductors. (C) 2001 Elsevier Science B.V. All rights reserved.